Surgeons who must cut through tissue to gain access to tissue create surgical trauma. The ability to access subcutaneous tissue with minimal trauma is a benefit to the clinician and patient. With the aging population and rising health care costs, any therapy that is less invasive, more effective, and less expensive has the potential to change the practice of medicine. Surgeons are continually looking for means to gain access to a broad cross section of tissue with as little cutting as possible.
The emerging field of regenerative medicine is becoming more prevalent. This field will require percutaneous access to a broad cross section of sub-dermal tissue to not only source cells but to also deliver therapy. For example, clinical trials that are underway or have been completed are documenting the clinical benefit of delivering stem cells from bone marrow and fat for numerous different disease states to include cardiac disease, vascular disease and bone and orthopedic disorders.
One tissue that is commonly used as a source of stem cells in the emerging field of regenerative medicine is bone marrow aspirate. Historically, marrow aspirate has been combined with matrix scaffold material to help form bone. Accessing bone marrow aspirate from the hip is cumbersome and time consuming.
Today, most marrow aspiration is performed to obtain a biopsy sample to determine if a person has a disease of the blood or marrow. Volumes required for the histology to make these determinations are less than 2 mL. Consequently, most marrow aspiration needles are designed to only capture enough volume for these kinds of tests from the iliac bone in the hip. Techniques exist for drawing large volumes of marrow for procedures such as bone marrow rescue therapy in cancer treatment, but drawing large volumes is not frequently done and is being replaced by stem cell harvesting from mobilized peripheral blood (that is to say, peripheral blood harvested after treatment with growth factors or other chemicals which stimulate a rise in the number of hematopoietic progenitor cells in the peripheral blood).
The volumes typically used for bone grafting cell therapy in support of regenerative medicine are greater than required for biopsy but less than required for bone marrow rescue therapy. The typical range of volumes for mixing marrow aspirate with bone scaffold matrix material is from 5 mL to 10 mL.
The typical volume of marrow aspirate for point of care cell therapy is between 50 mL and 400 mL. Marrow aspirate for use in cell therapy is typically volume reduced by 80% or more in an effort to concentrate the stem cells from the sample.
Marrow aspiration is usually obtained from the iliac crest bone. Bone is made up of a hard outer core known as cortical bone and a soft spongy interior known as trabecular bone with marrow filling in the porous space within the spongy bone.
Currently, to draw larger volumes of marrow, clinicians usually go into the hip bone through the iliac crest. The goal is to penetrate deep into the spongy bone and then to withdraw small aliquots of marrow as the needle is withdrawn. Traditionally, marrow aspiration is performed with an aspiration needle 100 (FIG. 1). This needle has two basic components: a component comprising a handle 104 with a luer connector 110 for attaching a syringe 106 on one end and a hollow metal tube or cannula 102 on the other end; and a component (not shown in FIG. 1) comprising a second handle attached to a solid metal rod or trocar with a sharp pointed tip. The trocar of the marrow aspiration needle is removable. When assembled, the second handle fits over the first handle and the trocar fits through the cannula 102, including the luer connector 110 and handle 104, such that the pointed tip of the trocar extends past the distal end of the cannula 102. This entire needle assembly is often referred to as a JAMSHIDI® aspiration needle. To perform a marrow aspiration, a clinical practitioner uses the fully assembled needle to penetrate cortical bone 110 using the point of the trocar. The clinician uses hand pressure or a mallet to tap the assembled aspiration needle through the bone. The cannula and trocar are usually made of stainless steel or titanium. The assembled aspiration needle is very hard and stiff so that the needle will not bend or buckle when longitudinal force is applied against the proximal handle to allow it to penetrate the cortical bone. Once the hard cortical bone 112 is penetrated, the assembled needle easily advances through the trabecular bone, including spongy marrow, 114. During insertion, the trocar is left in place to prevent the hollow cannula from becoming clogged with debris as the needle is pushed through the spongy marrow. Once the needle assembly is advanced sufficiently into the trabecular bone 112, the trocar, including the trocar handle, is removed to expose the luer connector 110. Luer connector 108 of syringe 106 is attached to the luer connector 110 of the needle and a vacuum created by pulling the syringe plunger will remove the marrow (FIG. 1). Marrow aspirate is pulled through the distal end of the cannula 102 and into the syringe 106 as the needle 100 is slowly removed from the marrow space 114.
A traditional bone marrow aspiration needle is typically used to access marrow from the hip or iliac bone. Because the traditional aspiration needle is stiff, the needle can only advance linearly within the marrow space. Thus, clinicians often need to perform multiple punctures in order to gain larger volumes of aspirate from a more diverse cross section of the marrow space. Since the hip bone is long and thin, once the traditional aspiration needle has penetrated cortical bone, the sharp and stiff instrument has the potential to penetrate through the other side of the cortical bone, resulting in significant trauma. Consequently, it is important for the surgeon to have a proper angle and skilled technique to ensure a safe aspiration. Since the iliac crest curves from the front to the back of the patient, the best angle of entry is from the back. Since the trocar is made of a stiff material, once inside the spongy bone, the needle assembly can only go straight, thus requiring multiple punctures to obtain the required volume of aspirate.
A traditional marrow aspiration needle is meant to access bone marrow from larger cavities and is not ideally suited to drawing marrow from the smaller confines such as the vertebral body of the spine. Because of the sharpness and stiffness of a traditional aspiration needle, using such an instrument in the small curved marrow space of a vertebral body would greatly increase the likelihood of introducing trauma. Less invasive and safer methods to access the marrow tissue of the vertebral body are needed in an effort to support the emerging field of orthobiologics. One fast growing area of this field combines marrow aspirate with synthetic matrix material in order to facilitate instrumented assisted spinal fusion.
Once fluid tissue is aspirated or otherwise sourced, the next step is to separate the nucleated cells that are present in the fluid tissue and concentrate them into a small volume so that they can be used clinically. For example, there are several commercial devices to separate and concentrate nucleated cells from aspirated bone marrow, fat, or cord blood. Some of these systems employ a floating insert or buoy that is meant to create an interface between the separated fluid components or fractions of interest. The challenge for any apparatus designed to accomplish such a task is the ability to volume reduce the fluid in which the nucleated cells are suspended while recovering as many cells as possible. For example, in marrow aspirate, approximately 1 to 2 percent of the cells suspended in the fluid are the target nucleated cells. Currently, no commercial device is able to consistently capture high percentages of nucleated cells while at the same time efficiently volume reduce (i.e. concentrate) the beginning fluid. In other words, no current device is able to simultaneously obtain a high yield and a high final concentration.
Therefore, a need exists for a bone marrow aspiration and separation system that can reduce or minimize the aforementioned problems.